"We saw no difference in pain at 3 or 7 days, no difference in return to the emergency department, no difference in hospitalization, and ultrasound decreased cumulative radiation exposure at 1 day and at 6 months," said Marshall Stoller, MD, of the University of California San Francisco.

Ultrasound performed by a radiologist or emergency physician led to serious adverse events in about 11% of cases, as did CT. Severe and attributable serious adverse events occurred in fewer than 1% of 2,800 patients and rates did not differ between patients evaluated by ultrasound or CT, Stoller and colleagues reported here at the American Urological Association meeting.

Given the potential cost savings and avoidance of radiation exposure, the decision about which imaging test to use should be pretty obvious.

"Ultrasound should be used as the initial imaging test," Stoller said. "Further imaging should be at physician discretion and based on clinical judgment."

Stone disease is often suspected when patients go to emergency rooms for evaluation of pain in the abdomen or flank. Abdominal CT has become the most common initial imaging study for evaluating patients for the presence of kidney stone, having supplanted ultrasound and intravenous pyelogram.

CT has a high sensitivity for diagnosing stones but confers a cancer risk associated with radiation exposure. Additionally, abdominal CT often leads to incidental findings and inappropriate referrals and treatment.

"Despite the higher sensitivity of CT, there is no evidence that it improves patient outcomes compared with ultrasound," Stoller said.

To compare outcomes with ultrasound or CT as initial imaging, investigators at 15 academic centers in the U.S. enrolled patients with suspected nephrolithiasis and randomized them to one of three imaging strategies: ultrasound by emergency physicians, ultrasound performed by radiologists, or abdominal CT.

After initial imaging, additional care was at the discretion of the treating physician, including other imaging studies, treatment, and disposition.

The primary outcomes were rate of complications from missed diagnoses, cumulative exposure, and total costs. After the initial visit in the emergency department (ED), follow-up continued at 3, 7, 30, 90, and 180 days. At each follow-up contact, study participants completed detailed structures interviews.

Stoller said investigators used the FDA definition of serious adverse events: untoward medical consequences that resulted in death, were life threatening, required hospitalization, caused significant morbidity, or required medical or surgical intervention to prevent permanent impairment.

Patients also were followed for occurrence of severe adverse events, subsequent serious adverse events that included abdominal aortic aneurysm with rupture, pneumonia with sepsis, appendicitis with rupture, bowel ischemic or perforation, renal infarction, pyelonephritis with urosepsis, ovarian torsion with necrosis, and aortic dissection with ischemia.

To determine cumulative radiation exposure associated with CT scans, Stoller and colleagues included the initial CT in the ED, subsequent CT studies during the first 6 months, number of series, volume CT dose index, and dose-length product (converted to millisieverts or mSv).

Each of the three imaging categories (ultrasound by emergency physician, ultrasound by radiologist, or CT) included more than 900 patients evaluated for suspected nephrolithiasis. Patients in all three groups had pain scores of about 8 on an 11-point scale, and the rate of hospital admission was 8% to 9% across the groups.

Stoller reported that 42% of the patients had a history of kidney stones, 63% had hematuria, 52% had costovertebral angle tenderness, and enrolling emergency physicians judged the patient had >50% chance of a kidney stone in 62% of cases. Men accounted for 51% to 53% of patients in each group.

Preliminary diagnosis of enrolling physicians was appendicitis in 3.6% of cases, abdominal aortic pathology in 0.8%, and bowel pathology in 3.6%.

Rates of serious adverse events ranged from 10.8% to 12.4% and did not differ significantly across the three groups. Similarly, severe events (0.2% to 0.7%) and attributable serious adverse events (0.3% to 0.5%) occurred in a similar proportion of patients in each group.

In 41% of the point-of-care ultrasound studies, patients subsequently had CT imaging, compared with 27% of patients whose ultrasound was performed by a radiologist, suggesting emergency physicians were less confident of their ultrasound findings.

Cumulative radiation exposure was 9 to 10 mSv in the two ultrasound groups versus 17.4 mSv in the CT group (P<0.001). Radiation exposure during the initial ED visit was 6.6 mSv with point-of-care ultrasound, 4.6 mSv with radiologist-performed ultrasound, and 14.2 mSv when CT was the initial diagnostic imaging test (P<0.001).

Duration of ED visit averaged about 8 hours and did not differ among the three groups. The proportion of patients who returned to the ED within 1 week was higher in the CT group (11.4% versus 9% to 10% in the other two groups, P=0.041).

The three groups also did not differ significantly with respect to the proportion of patients who returned to the ED within 1 month (15% to 16%) or within 6 months (28% to 29%). Hospitalization rates were similar at 1 week, 1 month, and 6 months.

The economic analysis of the study will be reported separately, but Stoller hinted at a large cost difference between the CT and ultrasound groups, noting that an abdominal ultrasound costs about $200 compared with about $4,000 for abdominal CT.

Patients eventually could tip imaging for suspected nephrolithiasis in favor of ultrasound, said Margaret Pearle, MD, PhD, of the University of Texas Southwestern Medical Center in Dallas.

"There is a tremendous amount of fear of radiation exposure, and a lot of patients say they don't want to be exposed to any radiation, even though the cancer risk with this amount of radiation is pretty insignificant," Pearle told MedPage Today. "Emergency physicians are very attuned to the fact that a lot of x-ray has been overutilized and patients are paying the price for it."

Financial considerations will probably figure into the decision to go with CT or ultrasound as the initial imaging test for suspected nephrolithiasis, she acknowledged. The large cost difference between CT and ultrasound has the potential to make emergency physicians at some centers feel pressure to order a CT, even if ultrasound can do the job just as well.

The study was supported by the Agency for Healthcare Research and Quality.

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